BusyBox developers go after Verizon

if they didn't install the software how did it get installed on the routers?

as far as 'first sale' goes, that applies when you are paying money for the software, but with
the GPL what you are paying is the promise to do specific things when you redistribute the
software to someone else. if you try to claim that 'first sale' privilages mean that you don't
have to follow through with your promises that would invalidate the GPL (and many other
licenses)